Check the USDA site for States beyond your own and you may be surprised to see plants listed in one area that are common in another. In Michigan we see carpets of spring beauty (Claytonia virginica) in the woods, a species that is endangered in Massachusetts. Great blue lobelia (L. siphilitica) and culver's root (Veronicastrum virginicum) are not deemed to be in any trouble in the Great Lakes States but the first is endangered in Massachusetts, and the other threatened.
Once you know this, it can be startling to see what you know to be an at-risk plant for sale at a garden center. For instance, purple coneflower (Echinacea purpurea) is one of the basic perennials stocked at garden centers all over the country, even in Michigan where that species is extirpated -- gone way beyond endangered to wiped out. The population of purple coneflowers that was in Michigan when European settlers first arrived has probably been completely lost. Any wild plants or seed involved in modern production of those plants come from regions where the plant is not in trouble.
In that example, the purple coneflowers you buy would not have been collected in Michigan. They do not have the genes that were particular to the Michigan portion of that species. (See genotype in our Scrabbling department.)
There is some controversy about whether we may further endanger an at-risk population when we plant what native plant growers can supply us -- plants of that species that are not of the local genotype. If the garden plants or their pollen escape to the wild, they may introduce "foreign" characteristics that don't suit local conditions or may further dilute an endangered gene pool.
Images above: Purple coneflower (Echinacea purpurea) has quite a bit of genetic diversity within its species. So there are many local genotypes, varying in flower form, height, bloom time and so on. Cultivated varieties -- cultivars -- abound. There is some concern among conservation specialist that introducing pollen from these clones into a wild poulation could dilute the local genotype.
Check around in your State or Province for more detail about plants on the list. For example, from the University of Michigan Herbarium website one can check by county where a given plant is reported to be established.